apes module 47 - photochemical smog and acid deposition

• describe the process of photochemical smog formation

  • Ozone forms during the daylight hours as NO2 breaks down in sunlight producing O which reacts with O2→ O3.
  • After sunset, the ozone will break down reverting to O2 and NO2. 
  • (c) When VOCs are present, the VOCs combine with nitrogen oxides during the day to form photochemical oxidants, which reduce the amount of ozone that will break down later and contribute to prolonged periods of photochemical smog.
• thermal inversion


  a warm layer of air covers a cooler, denser layer of air
• an inversion layer is a layer of warm air that traps emissions in thermal inversion
• air temperatures decrease by 3.5 degrees every 1,000 feet
• thermal inversion occurs when the ground rapidly cools; warm air rises and expands quickly, trapping the cooler layer beneath it. this may occur with blacktops
• thermal inversion may also be caused by upwelling
• thermal inversion traps pollutants
• Acid deposition occurs when nitrogen oxides (NOx) and sulfur oxides (SOx) are released into the atmosphere and combine with atmospheric oxygen and water; these form the secondary pollutants nitric acid (HNO3) and sulfuric acid (H2SO4)